Diameter-expandable annular degradable seal member for downhole tool, plug for well drilling, and method for well drilling

Abstract

A degradable seal member for downhole tools, the member being a diameter-expandable annular seal member, the diameter-expandable annular seal member comprising: two or more annular members distributed along an axial direction, the annular members being formed from a degradable polymer material having hardness in a range from A60 to D80; a plug for well drilling; and a method for well drilling using the degradable seal member for downhole tools.

The invention claimed is: 
     
       1. A degradable seal member for downhole tools, the member being a diameter-expandable annular seal member,
 the diameter-expandable annular seal member comprising: 
 three annular members distributed along an axial direction, wherein: 
 the annular members being formed from a degradable polymer material having durometer hardness in a range from type A (A60) to type D (D80), 
 of the three annular members, a center annular member and two end annular members of the annular members being adjacent along the axial direction, and 
 a length of the center annular member in the axial direction being 30 to 70% of a length of the diameter-expandable annular seal member in the axial direction. 
 
     
     
       2. The degradable seal member for downhole tools according to  claim 1 , wherein, in each of the polymer materials that form the two or more annular members, a difference in time taken for a decrease in 50% strain compressive stress of 50% strain compressive stress after immersion in 150° C. water relative to a 50% strain compressive stress before immersion to be not less than 5% is within 2 days. 
     
     
       3. The degradable seal member for downhole tools according to  claim 1 , wherein a loss rate of mass of the polymer material that form the annular members after immersion for 72 hours in 150° C. water relative to a mass before immersion is from 5 to 100%. 
     
     
       4. The degradable seal member for downhole tools according to  claim 1 , wherein the member polymer material that form the annular members is stable in a dry environment, and a decrease of 50% strain compressive stress after immersion for 6 hours in 23° C. water relative to a 50% strain compressive stress after immersion for 1 hour is less than 5%. 
     
     
       5. The degradable seal member for downhole tools according to  claim 1 , wherein the annular members have a tensile fracture strain at 66° C. of not less than 50%, a 70% strain compressive stress of not less than 10 MPa, and a compressive fracture strain of not less than 50%. 
     
     
       6. The degradable seal member for downhole tools according to  claim 1 , wherein, in the annular members, a ratio of compressive stress at 70% compressive strain relative to a compressive stress at 5% compressive strain at 66° C. is not less than 5:1. 
     
     
       7. The degradable seal member for downhole tools according to  claim 1 , wherein the diameter-expandable annular seal member is disposed on an outer circumferential surface orthogonal to an axial direction of a mandrel, and at least one annular member expands in diameter due to compression in an axial direction and plugs a gap between an inner wall of a downhole and the diameter-expandable annular seal member, and at least one other annular member has a function of blocking fluid by plugging a gap between the mandrel and the diameter-expandable annular seal member. 
     
     
       8. The degradable seal member for downhole tools according to  claim 1 , wherein the degradable polymer material contains at least one rubber material selected from the group consisting of urethane rubber, acrylic rubber, polyester-based thermoplastic elastomer, polyamide-based thermoplastic elastomer, natural rubber, isoprene rubber, ethylene propylene rubber, butyl rubber, styrene rubber, aliphatic polyester rubber, and chloroprene rubber. 
     
     
       9. The degradable seal member for downhole tools according to  claim 1 , wherein the degradable polymer material contains a polymer material containing a hydrolyzable functional group. 
     
     
       10. The degradable seal member for downhole tools according to  claim 1 , wherein the degradable polymer material contains a polymer material containing at least one urethane bond, ester bond, or amide bond. 
     
     
       11. The degradable seal member for downhole tools according to  claim 1 , wherein the degradable polymer material contains from 0.1 to 20 parts by mass of a degradation accelerator relative to 100 parts by mass of the degradable polymer material. 
     
     
       12. The degradable seal member for downhole tools according to  claim 11 , wherein the degradation accelerator contains at least one type selected from the group consisting of organic acids, inorganic acids, organic acid esters, inorganic acid esters, and acid anhydrides. 
     
     
       13. The degradable seal member for downhole tools according to  claim 1 , wherein the degradable polymer material contains a reinforcing material. 
     
     
       14. A plug for well drilling comprising:
 a mandrel, and 
 at least one degradable seal member for downhole tools described in  claim 1  disposed on an outer circumferential surface orthogonal to an axial direction of the mandrel. 
 
     
     
       15. The plug for well drilling according to  claim 14 , wherein the mandrel is formed from a degradable material. 
     
     
       16. The plug for well drilling according to  claim 15 , wherein the degradable material is polyglycolic acid. 
     
     
       17. The plug for well drilling according to  claim 14 , wherein the degradable material contains a reinforcing material. 
     
     
       18. The plug for well drilling according to  claim 14 , wherein the mandrel is formed from a composite material containing a degradable material. 
     
     
       19. A method for well drilling comprising: sealing a borehole using a downhole tool comprising the degradable seal member for downhole tools described in  claim 1 , and then the degradable seal member for downhole tools being degraded inside the borehole. 
     
     
       20. A method for well drilling comprising: performing a well treatment using a downhole tool comprising the degradable seal member for downhole tools described in  claim 1 , the degradable sealing member for downhole tools abutting another member for downhole tools, and then the degradable seal member for downhole tools being degraded inside the borehole.